Mediators in Service Data Objects (SDO)

While the datagraph provides the form of the data for SDO, (referred to as WDO for WebSphere^® Application Server version 5.x) the mediator provides the mechanism to move the data between a client application, such as a dynamic Web application, and a data source. Clients of the SDO run time use a mediator specific to the data source type to retrieve a datagraph. Clients can then work with the data contained in the graph and make changes. These changes can then be moved back to the data source using additional services of the mediator.

When a request is made to produce a datagraph, the mediator queries its targeted data source and transforms the result set into the SDO datagraph format. When a request is made to update an existing datagraph, the mediator extracts the changes made from the original state of the datagraph and returns those changes to the data source.

Some of the functionality common to SDO mediators includes:

A mediator is created with data source specific metadata.
The metadata defines the query to be used against the data source, as well as the structure of the datagraph that is produced by the mediator from the query result.
The mediator is stateless; after the datagraph is returned, it is removed from the mediator's memory.
A mediator can be directed to move the data from a modified datagraph back to the data source.

Note that you can find more information on Service Data Objects (SDO) on the Web by searching on the term, Eclipse Modeling Framework.